X-rays are used in oil and gas field tools for a variety of different applications. In one example, X-rays are used to evaluate a substance, such as a fluid or a formation. To this end, an X-ray generator is used to generate X-rays that pass through the substance. X-ray output of the X-ray generator is measured by a reference detector, while the X-rays that pass through the substance are measured by a second X-ray detector. The resulting signals from the reference detector and the second detector can be used to determine substance characteristics, such as density, porosity, and/or photo-electric effect.
In conventional systems, the reference detector uses a scintillator material to detect the X-rays. As the X-rays impact the scintillator material, the scintillator emits photons. In turn, the photons are detected by a photon detector, such as a photo multiplier tube (PMT). In this manner, a signal representative of the output X-rays is generated.
Such conventional reference detectors are difficult to use in oil and gas field tools. For example, one design constraint is that the reference detector is often placed immediately adjacent to the X-ray generator in order to more accurately measure output X-rays. Furthermore, to protect the reference detector from background and scattered X-rays, the reference detector is protected using a shielding material, which increases the package size of the reference detector. Such additional spacing and design constrains are particularly disadvantageous in downhole tools where available space is scarce. Also, the performance of scintillator detectors deteriorates as temperature fluctuates. This problem is compounded in downhole applications where environmental temperatures can be dynamic.